The present invention relates to a structure for coupling a wire grid type inorganic polarizer and a video projector including such a structure.
Recent video projectors project images with higher contrast. This has resulted in the need for improvement in image quality. To meet such a requirement, inorganic orientation panels are used as liquid crystal panels in a video projector. Further, instead of the conventional organic polarizers, which are arranged in front and behind a liquid crystal panel, wire grid type inorganic polarizers are now being used.
A typical type of polarizer is an absorptive type polarizer, which is formed from a polymer film containing iodine or a dye. The absorptive type organic polarizer has high polarization capability but absorbs light in a specific direction if it is not linear polarized light. Thus, the resistance to light (light resistance) is low with regard to light having short wavelengths such as ultraviolet light. Further, when light having a large light flux density strikes an organic polarizer, problems related to heat resistance may arise. For example, heat may accumulate and deform the polarizer. The dye may lose the color when heated. Accordingly, heat lowers the polarization capability.
An inorganic polarizer has high light resistance and thus has come into use in lieu of an organic polarizer. A representative example of an inorganic polarizer is a wire grid type inorganic polarizer. A wire grid type inorganic polarizer includes a wire grid formed by arranging elongated metal elements on a transparent glass substrate in intervals shorter than the wavelength of light. Refer to, for example, Japanese Laid-Open Patent Publication Nos. 2008-102183 and 2004-245871. A wire grid of metal elements has low mechanical strength. When wiped by a cloth, the wire grid may be damaged thereby adversely affecting the polarization function. To solve this problem, a surface protective coating may be applied to the metal elements. However, the surface protective coating would adversely affect the optical characteristics. For example, the light transmittance and absorptance may be decreased and the light reflectance may be increased. Further, the surface protective coating cannot protect the metal elements from an impact applied from the outer side by an object. Thus, in such a case, the metal elements may be damaged. To solve this problem, for example, the structure shown in FIG. 5 may be employed when using the conventional wire grid type inorganic polarizer.
In this structure, a polarization plate is coupled to a holder 101, which is used to facilitate coupling to a product and to adjust the coupling angle when coupled to the product. In the prior art example of FIG. 5, the holder 101 includes an opening 101a, which is used to couple the polarization plate. A wire grid type inorganic polarization plate 102 is inserted into the opening 101a. The wire grid type inorganic polarization plate 102 is set so that its glass substrate 102a is arranged at an outer side and its metal elements 102b are arranged at an inner side. A spacer 103 is arranged along the periphery of the glass substrate 102a. A surface protection glass plate 104 is fixed to the spacer 103 to seal the opening 101a opposite to the glass substrate 102a. The spacer 103 is discrete from the holder 101.
In this structure, the metal elements 102b are sealed between the glass substrate 102a and the surface protection glass plate 104. Thus, dust is prevented from collecting on the metal elements 102b. This eliminates the need to wipe the surface of the metal elements 102b. Further, impacts are prevented from being applied from the outer side by an object.
However, the structure of FIG. 5 uses a relatively large number of components. Further, additional work is necessary since the wire grid type inorganic polarization plate 102 and surface protection glass plate 104 are required to be inserted into the opening 101a of the holder 101 with the spacer 103 arranged in between. Thus, there is a demand for a simplified structure. Further, the polarization capability of a wire grid type inorganic polarizer is generally lower than that of a typical organic polarizer. Nevertheless, the wire grid type inorganic polarizer requires high precision machining and is expensive.